The present invention relates to a process for the preparation of ethyl trifluoroacetate. It relates more particularly to a process for the preparation of ethyl trifluoroacetate having a high purity.
Preparation of ethyl trifluoroacetate is described in the publication: Research Disclosure No. 24432. This publication discloses the preparation of trifluoroacetic acid esters by a 4-stage process according to which:
an alcohol of formula ROH, in which R represents an alkyl radical containing 1 to 5 carbon atoms, is condensed with trifluoroacetic acid in the presence of a strong inorganic acid (HCl, H.sub.2 SO.sub.4 or H.sub.3 PO.sub.4) at a temperature from 25.degree. to 110.degree. C.;
the mixture obtained is cooled and the aqueous phase is removed;
the organic phase is treated with concentrated sulfuric acid and/or phosphoric acid and the reaction between the acid and the alcohol is then continued at 25.degree.-110.degree. C.; and
the ester is isolated by distillation.
It has been found that when the reaction is carried out starting with trifluoroacetic acid and ethanol, this process does not enable an ester with a purity greater than 99% to be obtained in an economically profitable manner.
In fact, the esterification reaction is a balanced reaction according to the reaction scheme below: EQU CF.sub.3 COOH+CH.sub.3 CH.sub.2 OH.revreaction.CF.sub.3 COO CH.sub.2 CH.sub.3 +H.sub.2 O
To shift the equilibrium, an excess of one or the other of the starting materials may be used.
If an excess of ethanol is used, it can no longer be completely separated from the ethyl trifluoroacetate obtained because it forms an azeotrope with the latter which has a boiling point close to that of ethyl trifluoroacetate. If an excess of trifluoroacetic acid is used, the excess dissolves in part in the aqueous phase containing sulfuric acid, from which the trifluoroacetic acid is virtually impossible to extract when sulfuric acid is employed in small quantities. Since trifluoroacetic acid is an expensive starting material, it is advantageous to minimize its loss.
Consequently, the industry has been seeking for some time an economically profitable process for the preparation of pure ethyl trifluoroacetate.